1. Field of the Invention
The present invention relates to a method for inkjet printing suitable for preparing identification documents secured against alteration and for preparing graphic displays secured against graffiti.
2. Description of the Related Art
Identification documents are used on a daily basis to prove identity, verify age, access a secure area, evidence driving privileges, cash a check, make payments, access an automated teller machine (ATM), debit an account and so on. Airplane passengers are required to show an identification document (hereafter “ID document”) during check in, security screening, and prior to boarding their flight. Since they play a critical role in today's society, it is essential that ID documents cannot be falsified and are tamperproof.
Identification cards and documents, such as driving licenses, national or government identification cards, bank cards, credit cards, controlled access cards, and smart cards, carry certain items of information which relate to the identity of the bearer. Examples of such information or variable data include name, address, birth date, signature, and photo of the bearer. The ID cards or documents may in addition carry invariant data, i.e., data common to a large number of cards, for example the name of an employer.
Inkjet printing is very suitable for handling variable data. Also, due to the compactness of inkjet printers, it has become one of the preferred printing techniques for manufacturing ID documents. Inkjet printing can be used to assemble identification cards as disclosed, for example, in U.S. 2005/0042396 (DIGIMARC) using pigmented inkjet inks for printing the variable data, but it is also possible to use inkjet printing to introduce security features. In U.S. Pat. No. 6,837,959 (AGFA) inkjet printing is used to manufacture identification cards containing a watermark revealed by partial impregnation of a UV-curable lacquer into a porous, opaque ink-receiving layer.
Another security measure used in ID documents is the application of a transparent or translucent layer which is difficult or impossible to remove from the surface of the image-receiving layer, thereby sealing the data printed on the image-receiving layer. Such layers can be applied to ID documents using UV-curable liquids as disclosed in EP 0189125 A (INTERLOCK SICHERHEITSSYSTEME) and U.S. Pat. No. 5,614,289 (KONICA).
WO 01/32789 (3M INNOVATIVE PROPERTIES) discloses a cure-on-demand curable ink composition including a homogeneous mixture of at least one of: (a) a compound having 2 reactive silyl groups, and (b) a compound having at least 3 reactive silyl groups; an acid generating catalyst; and a pigment or pigment chip. The inks are improved for curing speed and outdoor weatherability, but nothing is mentioned about their use for preventing falsification of ID documents or graffiti on billboards.
Photocurable inkjet-inks including specific oxetane compounds are disclosed in U.S. 2004/0050292 (KONISHIROKU) and U.S. 2004/0052967 (KONISHIROKU), however both are silent on methods to prevent falsification of ID documents or graffiti on billboards.
However, the availability of cheap digital printing systems such as inkjet printers also led to a new type of fraudulent action on ID documents. Overprinting and over-labeling of the personalized information, such as the common “photo swap” method, allows easy and fast abuse of a stolen ID document.
Today, graphic displays such as point-of-purchase displays, billboards, banners, posters, and other outdoor signs are a favored surface for applying graffiti causing financial damage to the owners by unreadable commercial messages and replacement of the graphic displays.
One approach is to use a special type of ink-receiver having one surface made from abherent material. U.S. Pat. No. 6,626,530 (DU PONT) discloses a process for making an article with an image protected by a clear fluoropolymer film including coating the inner surface of the fluoropolymer film with a layer of hydrophobic, ink receptive polymer composition compatible with the fluoropolymer film. Other examples of fluoropolymer layers used in ink-receivers are disclosed in U.S. Pat. No. 6,001,482 (REXHAM GRAPHICS), U.S. Pat. No. 5,766,398 (REXHAM GRAPHICS), U.S. Pat. No. 5,795,425 (REXHAM GRAPHICS), U.S. Pat. No. 5,837,375 (REXHAM GRAPHICS), and U.S. Pat. No. 6,165,593 (REXHAM GRAPHICS).
Another approach is to apply a composition on the surface of an ink-receiver. U.S. Pat. No. 6,174,977 (TOYO INK) discloses a cold curable resin composition including a block copolymer of a polyorganosiloxane portion and a polymer portion having an epoxy group, a hydroxyl group, and a hydrolytic silyl group. The curable resin composition is coated preferably on a transparent base for imparting an anti-graffiti property or de-scribbling property to the surface of the base material.
High resistance to graffiti requires large amounts of polymeric abherent materials, preferably fluoropolymers having high molecular weight. Liquids used in inkjet printing require a very low viscosity, generally lower than 30 mPa·s resulting in liquids having concentrations of fluoropolymers insufficient for obtaining superior anti-graffiti properties.
Therefore, it would be highly desirable to be able to manufacture ID documents secured against alteration and to be able to protect graphic displays against graffiti using a simple manufacturing method and a compact apparatus.